1. Field of the Invention
The present invention relates to a built-in antenna and a method for improving antenna efficiency. More particularly, the present invention relates to a built-in antenna and a method for improving antenna efficiency in order to improve an antenna radiation property, to prevent radiation deterioration caused by a metal construction used to improve an outer appearance of a terminal, and to ensure mechanical robustness.
2. Description of the Related Art
With rapid technological advancement, a wireless communication function has been included not only in a mobile communication device but also in a portable electronic device (e.g., a media reproducing device, an electronic dictionary, a tablet, and the like), and the portable electronic device including such a wireless communication function has been used in everyday life. Portable electronic device users now prefer a smaller device having various functions. To satisfy the customers' preference, manufacturers are making an effort to decrease a size of components used in the portable electronic device and to integrate several functions into one component.
Such a change may occur equally in an antenna used to transmit and receive a radio wave. As a frequency band required for various services may be implemented by using one antenna, an effort to decrease a size of the antenna is ongoing.
A built-in antenna used in the portable electronic device of the related art is produced such that a metal layer is patterned on a circuit board so as to be used as an antenna radiator, or such that a metal sheet is patterned on a dielectric structure that supports an antenna radiator.
A Planar Inverted F Antenna (PIFA) and a monopole antenna are used as a built-in antenna widely used in a portable electronic device. These antennas have a disadvantage in that a performance-to-size relation cannot be designed in a complementary manner. More particularly, when a metal construction and a metal component are located near an antenna, there is a problem in that the antenna's radiation efficiency is decreased and a band is also decreased.
The portable electronic device of the related art has a sufficient space for placing an antenna and a sufficient separation distance to a metal portion. In addition, it is not difficult to design an antenna for the portable electronic device of the related art since an exterior of the portable electronic device is formed with a dielectric material, such as plastic. However, as the portable electronic device gradually decreases in size and thickness, a space for placing the antenna is being decreased, and a distance to the surrounding metal construction and metal component is being narrowed.
The aforementioned metal structure not only contributes to improving mechanical robustness but also improves the appearance of the portable electronic device. Therefore, there is an ongoing effort for applying this structure to a part of the portable device, more particularly, to a frame of the portable terminal.
However, it is difficult for the aforementioned built-in antenna of the related art to satisfy such a requirement as a compact size, efficiency increase, and a wide band in such extreme surrounding conditions.
In order to address this problem, antenna efficiency is implemented by using the antenna of the related art in such a manner that an antenna pattern is deployed by being spaced apart from a metal construction by a maximum distance possible in a narrow space for placing the antenna or that the metal construction existing at a portion where the antenna is located is processed with insert molding, or that a thickness of the portion where the antenna is located is increased. However, if an antenna pattern is deployed far from a metal component and a metal construction, a space for placing the antenna becomes further decreased and thus it becomes difficult to ensure more space. In addition, a method of performing an insert molding process on an antenna part impairs an outer appearance of the antenna since there is a disparity between metal and insert molding processes in a design aspect even if it is easy to ensure radiation efficiency. Furthermore, although radiation efficiency may be ensured by using a method of increasing a thickness of the portable electronic device, this method cannot make the portable terminal slim, which is a current design trend.
When the aforementioned metal construction is deployed in a front surface of the portable terminal, it has been used by being connected to a main ground. Such a structure exhibits a typical radiation deterioration phenomenon. That is, if there is a metal structure extended from the ground in the front surface of the antenna, a near field induces current in a corresponding metal member and generates thermal loss and radiation loss together with lossy volume, thereby resulting in an overall radiation efficiency deterioration.
To address such problems, a method in which a metal portion of an antenna is processed with insert molding and the remaining portions of a front surface of the antenna are subjected to metal processing has been used. However, this method has a problem in that a disparity occurs between metal and insert molding processes in a design aspect. A method in which the entire front surface of the device is subjected to metal processing and a distance between an antenna and the front-surface metal member is increased to the maximum extent possible by increasing a thickness of the terminal has a problem in that a slimming trend in the designing of the terminal cannot be satisfied. A method in which a front-surface metal member of a terminal is separated from a main ground can utilize the front-surface metal as a radiator, but may cause an Electro-Static Discharge (ESD) problem or a problem of radiation efficiency deterioration due to user influence.
Therefore, a need exists for a built-in antenna implemented to have a wide bandwidth and a method for improving antenna efficiency.